The long range objective of the work proposed is to provide researchers and clinical investigators with the capability to determine peptide hormones and neurotransmitters at ultra-trace levels in very small quantities of biological materials. In particular, a system will be developed that has several unique attributes which are critical to its generality. The system, meant for use as a detector for high pressure liquid chromatography (hplc), will detect any peptide. It will operate with such selectivity that only peptides will give a signal, and detection limits of one femtomole for ordinary hplc are expected. The discovery of new bioactive peptides, improvement in peptide hormone assays, deeper understanding of the roles of peptides in organs and systems, improvements in protein microsequencing and better pharmaceutical analysis will be a direct result of this work. The biuret reaction, long known as the basis of a method for protein determination, works for peptides. The biuret complex is oxidizable, so peptides can be detected electrochemically at an anode, as their biuret complexes, following their separation as native peptides. This is the basic chemistry that makes the proposed system instability of the oxidized biuret complex. The oxidized biuret complex can be detected at a cathode downstream of the anode. The current signal at the cathode will be an alternating one if the oxidized biuret complex is exposed to a chopped light source. The low detection limits will be a result, in part of the selectivity, and in part of carefully matching microelectrode array-based detection with the measurement electronics according to theory.